In sealing device for preventing the leakage of a sealed fluid, where the device comprises two parts configured so as to rotate relatively to one another and so that ends thereof slide on a flat surface, such as, for example, a mechanical seal, a balance must be struck the two opposing conditions of “seal tightness” and “lubrication” in order to maintain seal integrity for extended periods of time. In recent years, environmental concerns in particular have led to an increase in demand for reduced friction in order to reduce mechanical damage while preventing sealed fluid leakage. Friction can be reduced by reaching a “fluid lubrication state” in which dynamic pressure is generated between sealing faces due to rotation, and the surfaces slide with a liquid membrane interposed therebetween. However, in such cases, positive pressure is generated between the sealing faces, so that the fluid flows from the positive pressure area to the outside of the sealing faces. Such fluid outflow constitutes leakage in the case of a seal.
The inventors have already filed a patent application for a sliding member for a mechanical seal for sealing a sealed fluid present on one side in the radial direction of relatively rotationally sealing faces, wherein a plurality of grating portions 50, in which a plurality of parallel rectilinear indentations are formed on the sealing face at a predetermined pitch within a predetermined area, are circumferentially separated in the area between radii R2 and R3 on a sealing face 51 having an internal diameter R1 and an external diameter R4; the rectilinear indentations of the plurality of grating portions being formed so as to incline at a predetermined angle relative to the sliding direction of the sealing face, thereby improving the introduction and retention of the sealed fluid between the sealing faces, and allowing stable and favorable lubricity to be obtained, as shown in FIG. 7 (“the prior art”; cf. patent document 1).
The function of a mechanical seal is to act as a hermetic seal, and the path of the sealed fluid must be completely blocked when stopped in order to prevent leakage. To that end, an inner circumference 52 located on the atmosphere side of the grating portions 50 of the prior art described above is made to function as a seal dam area, preventing leakage while stopped.
The provision of the grating portions 50 in the prior art described above improves the lubricity of the sealing faces in the vicinity of the grating portions 50 from when rotation first starts, but the inner circumference 52 acting as a seal dam area tends to lack sufficient lubricity. The performance of actual testing confirmed that wear of the inner circumference 52 had occurred.